Lasmar made the comment while dismissing rumors that the problem might have been related to excessive physical training by the team in Russian Federation.
Brazil's next game at the tournament is next Monday afternoon's round-of-16 meeting with Mexico in Samara.
It says Marcelo is "undergoing treatment and showed good improvement", but it did not give a timetable for his recovery.
Filipe Luis will replace him in what will be the only change to the side that beat Serbia in their final group game. "Maybe the mattress in the hotel was softer than usual, but the key was it a bad move in the match", added Lasmar.
Boomers and Philippines match erupts in 'sickening' brawl that sees match abandoned
Australia met the Philippines for a matchup in Group B of the FIBA World Cup Qualifiers, but the game didn't go as planned. When Philippines captain Gabe Norwood fouled out, it left just one player available for the Philippines.
Brazilian team doctors blamed their hotel mattress for Marcelo's discomfort. "We are optimistic he can be used in the game", Lasmar said.
Manager Tite said: "I only know that he had a problem with his back. He said he locked up when he was leaving the pitch".
Winger Douglas Costa, who plays for Juventus, continues to recover from a right thigh injury he sustained in the group stage and will not play against Mexico.
Marcelo missed three Real Madrid matches due to a hamstring injury in February but has been otherwise largely injury free in recent years.